[keycloak-dev] Issue with concurrent SSO login to same client in more browser tabs

Hi, I've sent PR https://github.com/keycloak/keycloak/pull/5736 to fix the issue in subject (corresponding JIRAs are KEYCLOAK-7774 KEYCLOAK-8438). The cause is that once the user is authenticated in the browser and has userSession, there is just 1 clientSession per the userSession+client. So in case of concurrent SSO login in more browser tabs, there can be an issue that each tab is writing it's state to the same clientSession, which causes conflicts (especially attributes like nonce, scope or redirectUri can be possibly different for each tab and shouldn't be shared). The possibility can be to revert back when we had more clientSessions per userSession+client. I think this is step back and has lots of other issues (memory consumption, more cluster and cross-dc writes, worse performance in general...). For the future, it will be rather ideal to remove clientSession entirely or reduce their size even more, as they will be needed for logout, but hopefully for nothing more. So the other possibility is to move most of the state to the "code" parameter and to the refreshToken. Each browser tab has it's own "code" and it's own refreshToken. Problem with the "code" is, that it's used as query parameter in the URL and hence has limits for it's size. It seems ideal is still to stick with 2000 characters per URL. And when redirectUri itself will be part of the code, it can be problematic as we don't know how the redirectUri provided by users will be big.... Fortunately refreshToken doesn't have this issue as it needs to be always sent in the POST request. So to solve the issue for "code", I've added an entry to the infinispan cache "actionTokens", which encapsulates needed state and it's supposed to be valid just for the very short time (between the AuthenticationResponse to the application and the time when application sends the code-to-token request) and it's lifespan corresponds to realm code lifespan (1 minute by default). In the code-to-token request, there is a call to "cache.remove" to remove the code. Infinispan caches (local, distributed and hotrod caches) fortunately guarantee that "remove(123)" is always successful just in 1 thread (Successful means that it returns previous state). So we still have guarantee for the single-use code. Marek